JPS6321972B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking control method, and an object of the present invention is to provide a method for accurately detecting a track deviation from a track to be scanned by a rotary head during reproduction to perform tracking control.

In a helical scan type rotary head magnetic recording/reproducing device (hereinafter referred to as a VTR), there are variations in the tape guide groove formed on the fixed drum, variations in the inclination and height of the pole in the tape running system, and even the installation location of the fixed drum. Video track curvature inevitably occurs due to variations in the mechanism of the tape running system, such as angle variations. Therefore, when recording
The best tracking condition cannot be obtained during compatible playback when playing back on a VTR different from the VTR. Particularly in home VTRs, where the tape running system has been simplified to reduce costs, it is extremely difficult to play back while ensuring the required high tracking accuracy due to the high recording and playback density.
Also, the VTR that recorded and the VTR that played back
There may be a difference in the distance from the position where the rotating head starts contacting the magnetic tape to the control head, and in this case as well, the best tracking condition cannot be obtained and the SN ratio of the reproduced signal deteriorates.

Therefore, in the past, normal tracking was performed by adjusting the tracking knob and delaying the playback control signal by the required time, but this was done by moving the head scanning trajectory parallel to the longitudinal direction of one recording track. However, it was impossible to control the scanning so as to accurately follow the curve of a single track.

Therefore, in order to perform tracking control with higher precision, it is necessary to correct the track deviation by displacing the rotary head using a head moving mechanism in a direction perpendicular to the longitudinal direction of the recording track (in the direction of the track width). There is a need.

Conventionally, there have been two methods for detecting track deviations during tracking control, in which pilot signals with different frequencies are superimposed on the main information signal and recorded, and the tracks are reproduced separately from the tracks on both sides of the track to be scanned during reproduction. There was a method of detecting the track deviation direction and track deviation amount from the relative level difference of the pilot signals, but this method caused beat disturbance and also limited the band of the main information signal to be recorded and reproduced. I didn't like it.

On the other hand, a dither (wobbling) method has conventionally existed as a method for detecting track deviation without recording a pilot signal on a recording track. In this method, the rotary head is displaced upward in the track width direction using a sine wave with a short frequency synchronized with the rotary drum, and as shown in FIG. Draw a sinusoidal scanning locus shown respectively in
By detecting the difference in FM playback signal level,
It was designed to detect track deviation.

However, in this conventional dither method, in order to detect one track deviation, a point where the rotary head is shifted upward and a point where the rotating head is shifted downward are required. However, since the upper and lower detection points are the upper and lower peak points of the sinusoidal scanning trajectories 2a and 2b, there is a drawback that errors occur in track deviation detection due to locational differences. In addition, when a magnetic tape is recorded using the azimuth recording method, when the rotating head is oscillated in the track width direction, time axis fluctuations occur in the reproduced signal, which appears as curvature or uneven color on the reproduced screen. There were flaws. Furthermore, as the dither frequency becomes higher, the amount of shift information increases, but at the same time, there is a drawback that the time axis fluctuation further increases.

Furthermore, in the dither method, the head must be oscillated up and down, but in order to generate this head oscillation voltage, it is not necessary to use a phase-locked loop circuit that generates a signal several times the rotational frequency of the rotating head. However, the disadvantage was that the circuit configuration became complicated.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described with reference to FIGS. 2 and below. The present invention relates to a two-head helical scan system. FIG. 2 shows a block diagram of a tracking control system to which an embodiment of the present invention is applied. In the figure, 3 is an input terminal, and the frequency-modulated video signal is input to two terminals having different azimuth angles.
In FIG. 3, A ₁ ,
A reproduced FM video signal obtained by reproducing a magnetic tape recorded by sequentially forming tracks shown in B ₁ , A ₂ , B ₂ . Here, in FIG. 3, one track records one field of FM video signal. Reference numeral 4 denotes an input terminal through which a drum pulse, which is a symmetrical square wave as shown in FIG. 4A, is received, synchronized with the rotation of the rotary head, and having one cycle per rotation of the rotary drum, for example, as shown in FIG. 4A. This drum pulse is input to a pulse generator 7, which generates a sampling pulse as shown in FIG. Here, the sampling pulse is applied to the positions indicated by 1 to N, respectively, during the period when the rotating heads 17 and 18, which are disposed on the rotating drum 16 at positions facing each other at 180 degrees, are in contact with the magnetic tape as shown in FIG. It is output from the pulse generator 7 every time it passes through.

On the other hand, the reproduced FM video signal that has entered the input terminal 3 is supplied to the envelope detector 5, where the envelope is detected and then supplied to the sample circuit 6.

The sampling circuit 6 samples the reproduced FM video signal level at N locations of one recording track using the sampling pulse from the pulse generator 7,
The signals are sequentially taken out and applied to the memory 9. Memory 9 stores this level. On the other hand, the system controller 8 receiving the sampling pulse from the pulse generator 7 shifts the first field and the second field above the head as shown in FIG. 4C.
The third and fourth fields are connected to the first and second fields in order to shift the head downwards.
A + signal is given to the dither amount adder 11 for the field, and a - signal is given for the third and fourth fields. The dither amount adder 11 supplies an amount corresponding to the level required for the head oscillation to the memory 12 along with the oscillation direction indicated by + and - from the system controller 8. Output from memory 12 is provided to head moving mechanism 14. In this way, as shown in FIG. 4C, while the head swing signal, which is a rectangular wave generated by the system controller 8 and is inverted every two fields, is at a high level, the rotating heads 17 and 18 are operated by the head moving mechanism. 14, the rotary heads 17 and 18 are reproduced at a first height position higher than the reference height position, and while the head swing signal is at a low level, the rotating heads 17 and 18 are moved by the head moving mechanism 14 to a first height position higher than the reference height position. It is played at a lower second height position.

Therefore, for example, when the rotary heads 17 and 18 are at their respective normal height positions (i.e., zero track deviation)
The rotary head 17 rotates the sixth field when reproducing the first field.
The rotary head 18 scans slightly above the recording track ₁ , as shown at _17a1 in FIG. Then, when reproducing the next third field, the rotary head 17 moves to 1 in A of the same figure.
As shown by 7a ₃ , the area slightly below the recording track 1 is scanned, and furthermore, when the fourth field is reproduced, it is similarly scanned slightly below as shown by 18a ₄ . below,
The above operation is repeated. For convenience of illustration,
Although the track is shown as one track, it is important to note that each field is recorded on a different track.
As explained in the figure.

On the other hand, when the rotary heads 17 and 18 are shifted upward, a scanning trajectory shown in FIG. 6B is drawn, and when they are shifted downward, a scanning trajectory shown in FIG. 6C is drawn. Here, in FIGS. 6B and 6C, 17b ₁ and 17c ₁ are the first field reproduction positions of the rotary head 17, and 17
b ₃ and 17c ₃ are the third field playback positions of the rotary head 17, and 18b ₄ and 18c ₄ are the fourth field reproduction positions of the rotary head 18.
Indicates field playback position.

By the way, in a VTR, it is not possible to simultaneously obtain two scan trajectories, one above and one above, for a regular track.
Furthermore, in the case of a two-head VTR, it is not inconvenient to consider at least ten or more tracks played by heads of the same channel as exactly the same track. Therefore, by moving the rotary heads 17 and 18 up and down in the track width direction in units of one frame as described above, tracking information covering one track of two heads is obtained in a four-field section, and the tracking information at that time is obtained.
There is no problem even if the direction of track deviation is detected by comparing the FM video signal levels.

Control based on these detection results will be explained.

That is, as shown in detail in FIG. 7, in response to an instruction from the system controller 8, for example, during the first field and the second field, the switch S is tilted to the side a, and the data from the sample circuit 6 is accumulated. be done. The memory 9 stores data for two heads at 1 to N sampling points. Next, during the third and fourth fields, the switch S is turned to the b side, and the data from the sample circuit 6 is input to the comparator 10. here,
The sampling data of the first field input to the memory 9 and the third field input to the comparator 10 are compared, and similarly the data of the second field and the fourth field are compared. As a result, if the data are equal, the contents of the memory 12 are not changed. If the contents of the memory 9 are larger than the data input to the comparator 10, the system controller 8 gives a + signal to the dither amount adder 11, and the dither amount adder 11 changes the contents of the memory 12. . Also, if the contents of the memory 9 are smaller than the data input to the comparator 10,
The system controller 8 includes a dither amount adder 11
By applying a signal to , the dither amount adder 11 changes the contents of the memory 12 . Such operations are performed for each sampling point of the two heads, and the information obtained in the first four fields regarding the amount and direction of tracking the heads is input to the memory 12. Based on this information, the head control voltage generating circuit 13 receives the information in the memory 12 and drives the head moving mechanism 14 in the next four fields. In this way, the head scanning locus is controlled so that it becomes as shown by the dashed line or dashed line in FIG. 6A.

In this way, according to this embodiment, the rotary head is vertically moved (oscillated) in the track width direction in units of one frame, and the reproduced signal when scanning is shifted upward is transmitted to the N on one recording track. Track deviation is detected by storing data obtained by sampling at N sampling points in memory and comparing this data with N sampling data of the reproduced signal when scanning with the head shifted downward. , it is possible to eliminate the curvature and color unevenness of the reproduced screen that occur when reproducing an azimuthally recorded magnetic tape as in the conventional dither system. Furthermore, even if the head is shifted up or down, the sample points are always at the same location, so no errors occur in track shift detection.

As described above, the tracking control method according to the present invention adjusts the sample level at two or more sample points of the FM playback signal during one field period when one rotating head shifts upward or downward to perform scanning. The sample level of the FM playback signal during one field period and the sample level from the first memory when the first rotary head shifts downward or upward for each M field and performs scanning. A comparator compares the sample level at the same sample point among them, and calculates the value such that the two are approximately equal by comparing the sample level currently being played with the rectangular wave for moving the M rotary heads up and down for each M field. The signal obtained by adding and subtracting the head oscillation signal is stored in a second memory, and the head moving mechanism is driven and controlled based on the output signal of the second memory. It is possible to eliminate screen distortion and color unevenness caused by time axis fluctuations during tape playback, and since no pilot signal is recorded, there is no risk of limiting the recording/playback signal band or causing bead interference. Since the number of track samples N does not depend on the frequency of the head vibration signal, the amount of information can be increased by the desired amount, and since this sample point is at the same location on each track, errors that occur in track deviation detection can be avoided. Furthermore, since there is no need to provide a circuit that generates a signal several times the rotational frequency of the rotary head in order to generate the head oscillation voltage, the circuit configuration can be simplified.

[Brief explanation of the drawing]

Figure 1 is a track locus diagram of the conventional dither method.
FIG. 2 is a block system diagram of an embodiment of the tracking control system of the present invention, FIG. 3 is a track locus diagram on an azimuthally recorded tape, FIG. 4 is an output pulse diagram of each part of FIG. 2, and FIG. The figure shows a rotating head;
Fig. 6 is a track trajectory diagram of the present invention, and Fig. 7 is a track trajectory diagram of the present invention.
FIG. 3 is a detailed block diagram of the memory and comparator shown in FIG. 3...FM playback input terminal, 4...Drum pulse input terminal, 5...Envelope detector, 6...Sample circuit, 7...Pulse generator, 8...System controller, 9...Memory, 10...Comparator, 11...Dither amount addition 12...Memory, 13...Head control voltage generation circuit, 14...Head moving mechanism, 1
6... Rotating drum, 17, 18... Head, 19... Tape.

Claims (1)

[Claims] 1 Apply a head swing signal to a head moving mechanism in a magnetic reproducing device to displace M (M is a positive integer) rotating heads in a direction perpendicular to the longitudinal direction of a recording track on a magnetic tape. ,
In a tracking control method in which tracking deviation is detected based on the reproduction signal level of the rotary head and tracking control is performed based on the detection output, one field period when one rotating head shifts upward or downward during scanning. The sample levels at two or more sample points of the FM playback signal are stored in the first memory, and the sample levels of one field period when the rotary head shifts downward or upward and performs scanning for each M field are stored in the first memory. A comparator compares the sample level of the FM playback signal and the sample level at the same sample point among the sample levels from the first memory, and selects a value that makes both approximately equal to the sample level currently being played and the M A signal obtained by adding and subtracting a rectangular wave head swing signal for vertically moving each rotating head every M field is stored in a second memory, and the head moving mechanism is operated based on the output signal of the second memory. A tracking control method characterized by drive control.